astrolabe

astrolabe

(ăs`trəlāb), instrument probably used originally for measuring the altitudes of heavenly bodies and for determining their positions and movements. Although its origin is ancient and obscure, its invention is frequently ascribed either to Hipparchus or to Apollonius of Perga. For many centuries it was used by both astronomers and navigators. A simple astrolabe consisted of a disk of wood or metal with the circumference marked off in degrees. It was suspended by an attached ring. Pivoted at the center of the disk was a movable pointer called by Arab astronomers the alidade. By sighting with the alidade and taking readings of its position on the graduated circle, angular distances could be determined. Mariners, if sufficiently skilled in navigation, could use the astrolabe to determine latitude, longitude, and time of day and as an aid in making other calculations. It was much used on voyages of discovery in the 15th cent. and was important until the invention of the sextant in the 18th cent. The more elaborate astrolabes bore a star map (the planisphere, a circular map, was added by Hipparchus), a zodiacal circle, and various other useful or decorative devices.

astrolabe

(ass -trŏ-layb) An instrument, dating back to antiquity, used to measure the altitude of a celestial body and to solve problems of spherical astronomy. From the 15th century it was employed by mariners to determine latitude, until replaced by the sextant. There have been various types of astrolabes. One simple form consisted of a graduated disk that could be suspended by a ring to hang in a vertical plane. A movable sighting device – the alidade – pivoted at the center of the disk. Modern versions are still used to determine stellar positions and hence local time and latitude. See also prismatic astrolabe.

Astrolabe

(religion, spiritualism, and occult)

An astrolabe is a mechanical device that, prior to the development of the sextant, was widely used by mariners. Said to have been developed by Hipparchus, greatest of the ancient Greek astronomers (although some scholars give Ptolemy the honor), the astrolabe was used by astrologers when they erected horoscopes to determine the positions of the planets. (Prior to the development of ephemerides, it was necessary to actually look at the heavens when casting a horoscope.). The term astrolabe means “taking the star” in Greek, so it could be used to refer to any instrument for observing the stellar dome. Thus, in the early medieval period, astrolabe was often applied to the armillary sphere, a different instrument. The device now called an astrolabe is more properly termed a planispheric astrolabe. Originally Greek, this instrument was lost to western Europe until its reintroduction by Arabic sources.

Sources:

Tester, Jim. A History of Western Astrology. New York: Ballantine, 1987.

Astrolabe

a bay on the northeast coast of New Guinea (Maclay Coast). The bay is about 37 km long and 34 km wide, with depths of 40–106 m. The coast is hilly and covered with tropical vegetation. Many points on the coast have Russian names—for example, Konstantin Harbor, Cape Novosil’skii, Cape Koptev, and the Gogol River—as a result of the work done by the Russian traveler N. N. Miklukho-Maklai in New Guinea.

astrolabe

[′as·trə‚lāb]

(engineering)

An instrument designed to observe the positions and measure the altitudes of celestial bodies.

astrolabe

an instrument used by early astronomers to measure the altitude of stars and planets and also as a navigational aid. It consists of a graduated circular disc with a movable sighting device

Complicated weather systems like the polar vortex make it hard to say how climate change will continue to play out, in the Arctic or elsewhere--a conundrum that frustrates researchers like Astrolab manager Vivek Voora.

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